The present invention relates to a device for recovering hydrogen generated by decomposition of hydrocarbon gas with steam.
Hydrogen has been used in broad industrial fields as basic raw material in a chemical industry, a fuel for a fuel cell or an atmospheric gas for heat treatment. A representative process to cope with a small demand is decomposition of hydrocarbon gas with steam. A decomposition product contains CO, CO2 and residual H2O other than H2. The product cannot be used as such for a fuel cell due to the inclusions; otherwise faculty of the fuel cell would be degraded. In this regard, it is necessary to remove subspecies such as CO, CO2 and residual H2O, before the reformed product is supplied to a fuel cell.
A conventional method of removing subspecies uses a hydrogen-permeating membrane made of such a catalytic element as Pdxe2x80x94Ag or Ta selectively permeable to hydrogen. The hydrogen-permeating membrane has been formed so far as a thin layer on a heat-resistant perforated body, as disclosed in JP 63-294925 A1 and JP 1-164419 A1. Recently, feasibility of a perforated metal body, in which a plurality of holes are formed for passage of hydrogen has been studied instead of a conventional heat-resistant perforated body.
A perforated metal body coated with a hydrogen-permeating membrane is attached to a surface of a hydrogen-recovering device, to which a takeout pipe is coupled, and embedded in a catalyst layer. Hydrogen gas generated by decomposition of hydrocarbon gas with steam selectively passes through the hydrogen-permeating membrane into the hydrogen-recovering device and flows through the takeout pipe to the outside.
A conventional hydrogen-recovering device uses a thick plate as a structural member in order to inhibit thermal deformation caused by heat cycles between high and ordinary temperatures. As a result, the device is heavy, and a special fixing jig is necessarily used for fixing the device in a reforming plant at a predetermined position. The thick plate is processed by etching, machining or electric discharge machining to form holes for passage of hydrogen and a header, and then a hydrogen-permeating membrane such as a Pdxe2x80x94Ag alloy is laser-welded to an external surface of the thick plate. Such processing is troublesome and inappropriate for mass-production at a low cost.
The present invention aims at provision of a new hydrogen-recovering device, which is light and strong, easy to manufacture by using a thin steel sheet press-worked to a predetermined shape as a structural member.
The present invention proposed a box-shaped or tubular hydrogen-recovering device having a frame made of a ferritic stainless steel.
The box-shaped hydrogen-recovering device has a box-shaped frame made of a ferric stainless steel having a takeout pipe attached to its one side, a plurality of spacers arranged along a lengthwise direction inside said box-shaped frame, perforated metal plates fixed to both surfaces of said box-shaped frame, a hydrogen-permeating membrane clad with a membrane holder fixed to said perforated metal plate, wherein hydrogen gas as a decomposition product of hydrocarbon selectively passes through said hydrogen-permeating membrane and flows to the outside.
The tubular hydrogen-recovering device comprises a pair of upper and lower discs each of which has an opening for passage of hydrogen at its center, a plurality of reinforcement members which extend between said upper and lower discs and locate with the same intervals along a circumferential direction, perforated metal plates which is fixed to a cylindrical surface defined by curved surfaces and end faces of said reinforcement members and is coated with a hydrogen-permeating membrane, and a takeout pipe coupled to one or both of said upper and lower discs, wherein hydrogen passes through said hydrogen-permeating membrane into a cavity inside said perforated plates and flows through said takeout pipe to the outside.
The members other than the hydrogen-permeating membrane are preferable made of a ferritic stainless steel which has a thermal expansion coefficient near that of the hydrogen-permeating membrane.